Just picked up a 95 Jimmy and while investigating loud exhaust found the cat missing, my question is : would this cause hesitation in normal acceleration and poor engine performance? by that I mean higher than normal gas consumption. It would seem to me that the o2 sensor behind the cat would give incorrect reading to the computer?
The O2 sensor behind the cat's are not used to calculate the A/F ratio, the left and right bank do. The O2 sensor behind the cat only monitors the performance of the cat. The missing cat's will cause you to have poor performance and poor fuel economy, the engine does not have enough back pressure and is throwing off the sensor readings to your PCM.
Your engine runs on vacuum sensor's, that's why a larger Cam will hurt the performance of a Vortec unless the PCM has been re-tuned for the lower internal vacuum. The back pressure also helps seal the valves in the higher RPM to help keep the compression ratio as high as possible.
I did put a high flow Cat and had to re-tune my PCM for a more aggressive timing then the stock to compensate for the less back pressure i have now. In the old school days of no cats and duel exhaust with larger exhaust pipes, the carbs were run richer and the timing was turned as far in advance just enough to get it to start without any backfire through the carbs.
With today's electronic controlled engine's, there is really not much we can do. Unless you can re-tune your engine to match any mods you have done that may be beyond the parameters of the PCM programs.
Hope this helps and keep us posted, Maganflow has a few after market Cats that can bolt right in place. Just call them up for the right application for your 4.3 Vortec, and your good to go. Still be a high flow, but within the PCM program to your 1995 Jimmy.
